In the push to scale CNT FET electronics from long channel optical lithography to short channel deep ultraviolet (DUV) lithography of 0.5 microns, the device contact length needs to be reduced to less than 1 micron. In the state of the art CNT FET, a thin adhesion layer of titanium (Ti) is capped with palladium (Pd) metal as an ohmic contact to a CNT array. This Ti layer is necessary for adhesion of the Pd to the CNTs, but the Ti layer has a lower work function then the CNT array, thus resulting in a barrier at each contact point. In the state of the art, it has been shown that the Ti layer hinders channel scaling of less than 1 micron. If the Ti layer is removed from the stack, channel scaling of less than 1 micron can be measured but the lack of adhesion between the Pd and the CNT array (e.g., on quartz) results in a yield of less than 10%.
A Co—C eutectic metal alloy as a ohmic contact fixes both of these problems. A Co—C eutectic metal alloy adheres to the wafer without a need for an adhesion layer. In contrast to the use of the high work function metal Pd, the use of a Co—C eutectic metal alloy comprising the high work function metal Co allows the Co—C eutectic metal alloy to be in direct contact with the CNTs and thus reduce the barrier on the contact. Thus, the Co—C eutectic metal alloy enables contact scaling of less than 1 micron with great adhesion resulting in yields above 75%.
While the work function of Co has been catalogued, it has not been applied to CNT FET's as an ohmic contact or part of the composition of an ohmic contact due to the difficulty in integrating the process. In embodiments herein, Co—C eutectic metal alloy ohmic contacts utilize the solubility of C into Co as a way to stabilize the deposition technique allowing for easy integration via electron beam evaporation.